Anti-stain treatment for water-repellent coated lumber in transit

ABSTRACT

Disclosed are methods and compositions for preventing or minimizing staining of lumber having a water-repellent coating thereon, during transit, particularly during rail and ship transit, under conditions of exposure to iron contaminants by adhering to the coated surface of the lumber an essentially atinctorial deposit of exposed particles of a slow-leaching base in an amount sufficient to maintain the coated surface of the lumber at a pH at about 10 or above for the period of transit.

United States Patent 1191 Story 1 ANTI-STAIN TREATMENT FORWATER-REPELLENT COATED LUMBER IN TRANSIT [75] Inventor: Laurence A.Story, Burnaby, British Columbia, Canada [73] Assignee: SCM (Canada)Ltd., Toronto,

Ontario, Canada Notice: The portion of the term of this patentsubsequent to Sept. 4, 1990, has been disclaimed.

[22] Filed: May 22, 1972 [21] Appl. No.: 255,860

Related US. Application Data [63] Continuation-impart of Ser. No.142,791, May 12,

1971, Pat. N0. 3,756,850.

1*Apr. 30, 1974 1/1946 Hill 117/149 1,556,570 10/1925 Coolidge 117/1492,799,597 7/1957 Walker et al. 117/149 3,393,122 7/1968 Marshall 21/73,180,746 4/1965 Patton et a1. 117/147 3,180,747 4/1965 Patton et a1.117/147 2,357,725 9/1944 Bennett 117/147 Primary Examiner-MichaelSofocleous Assistant ExaminerWil1iam R. Trenor Attorney, Agent, orFirm-Merton H. Douthitt; Richard H. Thomas [5 7] ABSTRACT Disclosed aremethods and compositions for preventing or minimizing staining of lumberhaving a waterrepellent coating thereon, during transit, particularlyduring rail and ship transit, under conditions of exposure to ironcontaminants by adhering to the coated surface of the lumber anessentially atinctorial deposit of exposed particles of a slow-leachingbase in an amount sufficient to maintain the coated surface of thelumber at a pH at about 10 or above for the period of transit.

10 Claims, No Drawings 1 ANTI-STAIN TREATMENT FOR WATER-REPELLENT COATEDLUMBER IN TRANSIT This application is a continuation-in-part of US.application Ser. :No. 142,791 filed May 12, 1971, now US. Pat. No.3,756,850 the disclosure of which is incorporated by reference.

This invention relates to methods and compositions especially adaptedfor coating water-repellent treated lumber to prevent staining of thecoated lumber during transit and subsequent storage periods. Morespecifically, this invention relates to compositions and methods forpreventing or controlling the degradation of lumber through colorchanges resulting from undesired chemical reactions.

An unusual problem has been encountered when the freshly cut lumber istransported great distances by rail under conditions where the lumber isexposed to rain, snow, mist, dew, fog, salt water and sunshine and otherelements of weather. Under these conditions, the lumber is observed todarken to a brown or black color. This darkening condition is known railtransit stain or merely transit stain. Up to now, transit stain wasaccepted as an inherent problem in the transportation of lumber by rail.To a lesser extent, transit stain forms on lumber transported by rail ortruck when the lumber has a prior history of rail transit-Apparently aircurrents carry iron dust from the rail car wheels and the brake carshoes to the lumber. Staining will begin when atmospheric moisture suchas rain or dew contacts the iron-contaminated wood. Thus, if no moistureis encountered during transit, staining could develop upon exposure tomoisture while sitting in a lumber yard after exposure to iron dustduring transit. The iron dust which was deposited during transit did notcause the immediate darkening because sufficient free moisture was notavailable for the reaction to proceed. Accordingly, there is a need toprotect lumber from transit staining for at least the period of transit,and if necessary'for the period of storage thereafter. For practicalpurposes, then, it is often necessary to protect lumber from transitstaining over a period of up to three months. v

Freshly cut or green lumber from trees such as redwood, cedar, spruce,fir, pine and hemlock contains wood acids, tannins, lignins and otherchemicals which react with environmental chemicals to form new compoundsthe color of which are generally unlike that of freshly cut lumber.Green lumber is rather acidic in nature due to the relatively highcontent of wood acids and when wetted by rain, forms a suitable vehiclefor dissociation of certain metals, such as iron, into their ionicstate. When this occurs, certain chemical reactions result which producechemical discoloration on the lumber surface wherein the lumber becomesdarkened. Continued exposure of the wood allows the reaction topenetrate the surface and at the same time increases the discolorationon the surface.

One method of preventing transit staining is to wrap the lumber withpaper or other protective covering material to physically shield thelumber from the elements. This method is time consuming, costly,inconvenient, and undesirable from an ecological point of view becausethe wrapping materials, which are often tar or asphalt impregnated, mustbe burned or otherwise disposed of.

Attempts have been made in the past to prevent transit staining byproviding the lumber with a waterrepellent coating. It was theorizedthat the waterrepellent coating would keep the moisture from contactingthe wood and thereby prevent the chemical reaction responsible for thetransit stain. While this approach is apparently theoretically sound, ithas not been successful from a practical standpoint because transitstain has been observed on lumber treated with water-repellent coatings.The observed transit stain on water-repellent treated lumber is not assevere as in the case of untreated lumber, but it nevertheless rendersthe lumber unsuited for many commercial applications.

The reason for the lack of success of the waterrepellent coating is notunderstood, although it is suspected that the water-repellent coating isnot a continuous film and moisture reaches the wood through flaws anddefects in the coating and transit stain results. For example, a railcarload of lumber that has been treated with a waxy type water-repellentcoating was observed to have discrete areas of transit stain. Theseareas are formed when drops of water accumulate on the waterrepellentcoating. Due to the nature of the waterrepellent coating, the dropletsbead up on the coated surface of the lumber. When these beads evaporate,a definite area of transit stain remains where the beads had been.

Despite these disadvantages in the water-repellent treatment approach topreventing transit stain, many lumber people believe thatwater-repellent coatings have sufficient advantage from otherstandpoints (i.e., protecting the dimensional stability of the lumber)that the water-repellent coatings are justified. Accordingly, thepresent invention provides a method for preventing transit stain on suchwater-repellent treated lumber.

As used herein, the term water-repellent coating" refers to coatingsthat cause water to bead up" and form droplets rather than spread out asa film. Such water-repellent coatings include the conventionalthermoplastic and thermosetting resinous polymers (includinghomopolymers, copolymers, terpolymers, etc.), resinous coating such aspolyolefins (e.g., polyethylene, oxidized or emulsified polyethylene andpolypropylene); natural or synthetic waxes such as paraffin wax,carnauba wax and petroleum wax; metallic salts of fatty acids such aszinc and aluminum stearates, octoates, and palmitates; ammonical zinccompositions, modified or unmodified polyesters (e.g., the ethyleneglycol/maleic/phthalate styrene type and glycerol phthal ate typeincluding those known as alkyds); shellac; petroleum resins; naturalresins; epoxide resins, phenol formaldehyde resins; allyl resins;polystyrene resins; polyamides such as nylon; vinyl resins such aspolyvinyl chloride, polyvinylidene chloride, polyvinyl acetate,polyvinyl-chloride-polyvinyl acetate resins, vinyl chloride-styreneresins, vinyl chloride-butadiene resins, vinyl chloride-acrylonitrileresins; acrylic acid and acrylic ester polymers such as polymethylmethacrylate, and methyl methacrylate-styrene; acetal polymers andcopolymers; chlorinated rubber; acrylonitrilcbutadiene-styrene polymers;isoprene polymers; butadiene-styrene copolymers; polyvinyl butyralresins; styrene-ethylene copolymers; polyfluorocthylene rcsins,polyvinylidene fluoride resins and polyurethane resins.

These resins are applied to the lumber to form waterrepellent coatingsin the form of solvent solution (e.g., in aromatic hydrocarbons such astoluene and xylene; aliphatics such as hexane, octane or evencycloaliphatics such as cyclohexane; alcohols such as methanol andethanols; or even in solution in a vinyl monomer polymerization withethylenic unsaturation present in the film-forming resins), watersolution or aqueous latex depending on chemical and physical conditions.

Several latices used for water-repellent coatings for lumber areavailable commercially. These include butadiene-styrene latices (Latex512R, Dow Chemical) containing 35 to 55 percent total solids; vinylchloride latices containing 50 to 55 percent total solids; vinylidenechloride-acrylonitrile copolymers (Saran Fl22-Al5, Dow Chemical);polystyrene latices containing 35 to 45 percent solids; vinyl esterlatices such as polyvinyl acetate containing 40 to 55 percent totalsolids (Gelva S-55, Shawinigan); latices of polyvinyl acetate-polyvinylchloride (resyn 2507, National Starch) containing 40 to 50 percent totalsolids; butadiene-acrylonitrile copolymers (Hycar 1577, Goodrich);styrene-acrylonitrile latices, polymethymethacrylate latices andbutadiene-acrylie ester latices. The latices usually have an averagemolecular weight in the range of about 25,000 to about 100,000. Thechemical nature of the water-repellent coating is not significant andthe present method prevents transit staining in all types ofwater-repellent coatings on lumber.

in my Canadian Pat. No. 756,052, a method is disclosed for keeping thelumber surface at an acid pH such as with oxalic acid so that theappearance of freshly milled wood remains for an extended period oftime. The oxalic acid reacts with contaminants to form oxalate saltswhich closely approximate the color of wood. Unfortunately, some oxalatesalts are water soluble and with heavy rain the oxalate salt may bewashed away leaving the wood susceptible to further staining. Thus, thepresent invention represents an advance over my Canadian Pat. No.756,052 in providing a different mechanism for preventing travelstaining.

US. Pat. Nos. 3,333,977 and 3,333,978 propose acidic anti-stainingcoating for redwood and cedar comprising certain polyester resinstogether with water-soluble salts, oxidizing agents, organic peroxidesand water-soluble acids for prevention of sap staining. This proposaldoes not apply to and is not effective against transit stain.

U.S. Pat. No. 3,565,681 concerns a method of preparing anti-rust paperfor use as labels on metallic containers. These anti-rust papers areprovided with a coating of calcium hydroxide, water-dispersible adhesivecompatible with the calcium ions and selected from the group consistingof starch, protein, synthetic binder and mixtures thereof. This patentdoes not concern the problem of transit staining on lumber.

US. Pat. Nos. 2,818,344; 3,085,893 and 3,033,700 disclose the use ofcertain barium borate pigments in paints for the purpose of promotingcleaner, longerlasting films. The films are of the paint type whichencapsulate the pigment so that the pigment is not exposed to theelements but rather is embedded in the paint film. These patents do notdiscuss the formation of transit stains on lumber or the prevention ofstain. The barium borate pigments disclosed in these three patents areused in the percentage of 2 to 20 percent of the paint for the purposeof inhibiting mold growth. The barium pigments disclosed in these threepatents are suitable for use as alkaline-earth base in the practice ofthe present invention, and accordingly the teachings of these threepatents is incorporated by reference.

It has now been discovered that this rail transit stain can beeliminated or materially reduced in lumber having a waterrepellentcoating thereon by adhering to the exposed coated surfaces of saidlumber at an exposed essentially atinctorial deposit of a particulatebase which is slowly leachable upon exposure to atmospheric moisture toproduce a basic extract solution having a pH of about 10 or greater. Thedeposit is adhered to the water-repellent coating lumber in an amountsufficient to maintain the pH of at least a sub stantial portion of theexposed surface above about 10 for the period of transit. Thus, thepresent invention is completely contrary to the prior methods ofmaintaining the freshly cut appearance of the lumber wherein the woodsurface was maintained at an acid pH to prevent staining. The binder isused merely to fasten or glue the base particles to the water-repellentcoated lumber and keep the particles from being physically dislodged bythe forces of handling or shipping or by the physical force of the windand rain.

The deposit is in no sense of the word a paint because the deposit isintentionally binder starved" or pigment rich so that the depositparticles are exposed for leaching with atmospheric moisture. Paint hasbeen defined as a pigmented liquid composition which is converted to anopaque solid film after application as a thin layer.

In the context of the present invention, it is more appropriate to thinkof the binder as an adhesive to distinguish from the term binder as itis used in describing paint films. In fact, an adhesive which is alsowater repellent is ideal so that it will not be washed away during heavyrainfalls.

The exact chemical mechanism responsible for the effectiveness of thepresent invention is not completely understood, although it is stronglysuspected that the actual cause of transit staining in lumber is thechemical reaction occurring between the wood acids, tannins and otherchemicals in the wood with the ambient iron contaminants that penetratethe waterrepellent coating in the presence of atmospheric moisture toproduce brown or black iron compounds on the lumber surface.Surprisingly, iron oxide in pigmentary form as ferric oxide does notreact with the wood to form discolored products. In fact, yellow and rediron oxide pigments can be used to tint the inventive coating to closelymatch the wood color. Apparently, only metallic iron is responsible fortransit staining.

The iron contaminants come from the iron and steel transportationequipment. For example, railroad car brakes under friction releasesignificant quantities of 'iron particles in the form of dust. Thefriction of the steel railroad wheels on the railroad .tracks can resultin the release of metallic iron dust. Moreover, steel transportationcompartments as well as the chains and straps for securing the lumber tothe compartment are sources of iron contaminants. In the presence ofrain and moisture, these iron contaminants react with the wood acids toproduce the brown or black stain on water-repellent coated woodsurfaces. Whatever the exact chemical mechanisms, the freshly cut lumbercan be less than about 50 percent by weight at 32F. but' greater thanabout 0.001 percent). If the base were too water soluble, the depositwould be dissolved during the first rain to leave the water-repellentcoated lumber unprotected for the remainder of the period of exposure,although this may be acceptable for short periods of exposure.

The term atinctorial as used herein means that the base does not have atendency to react with the wood to tint it from its natural color. Inother words, the base is neutral with respect to color, althoughcolorants and tints can be added to the coating composition for thepurpose of color coding or to highlight or approximate the natural colorof the lumber.

The term base refers to a compound which yields hydroxy ions in aqueoussolution. These base particles due to the slight or moderate solubilityare slowly leachable with atmospheric water to form a basic buffersolution which prevents the iron from reacting with the wood chemicalsto form a stain. Usually at least a portion of and preferably all of thebase particles have solubility in water of less than about percent byweight at 32F. and preferably less than 1 percent at 32F.

When the water-repellent coated lumber requires protection for prolongedperiods of up to several months, at least a portion and preferably allof the base particles having a water solubility of about 0.001 percentto about 0.5 percent by weight are particularly effective so that theparticles are very slowly leachable with atmospheric moisture to yield abuffer solution on the surface of the lumber throughout the period ofexposure.

Suitable atinctorial slowly leachable bases are alkalineearth metalbases which include oxides, carbonates, phosphates, hydroxides, borates,borosilicates and hydrates of the same of the alkaline-earth metalsmagnesium, calcium and barium such as barium oxide (BaO), bariumcarbonate (BaCO barium hydroxide [Ba(OH) barium hypophosphate (BaPObarium monohydrogen orthophosphate (BaHPO barium metasilicate (BaSiObarium orthoborate (3BaO B 0 barium metaborate (BaO B 0 bariumoctaborate (BaO 4B O barium borosilicate (3BaO 33 0 2SiO magnesiumcarbonate (MgCO magnesium carbonate hydrates (MgCO 3H O and MgCO 5H O)and other barium borates and barium borosilicates described in U.S. Pat.No. 2,818,344; basic magnesium carbonate [MgCO Mg(OH) 3H O and 3Mg0Mg(OH) 3H O], magnesium oxide (MgO), magnesium acid carbonate (MgHCOmagnesium hydroxide [Mg(OH magnesium orthophosphate [Mg (P0,) 4H O],magnesium monohydrogen orthophosphate [MgHPO 3H O]; calcium tetraborate(CaB,O calcium carbonate (CaC0 calcium hydroxide [Ca(OH) calcium oxide(CaO), calcium orthophosphate [Ca (PO calcium monohydrogenorthophosphate (CaHPO 2H O), calcium metaborate (CaB O calciummetaborate hexahydrate (CaB O 6H O). Other slow leaching bases includetrisodium phosphate, sodium carbonate, sodium sesquicarbonate, borax andsodium bicarbonate. These slow-leaching bases are often used tosupplement the alkaline-earth bases.

The particle size of the base particles is not particularly critical aslong as the particles are in the size range generally used forpigmentary purposes. The average particle size for these purposes isusually less than 50 microns and preferably about 1 micron to about 15microns. The bases can be supplemented with watersoluble bases (i.e.,those bases having a solubility in water in excess of 50 percent byweight at about 32F.) such as sodium and potassium hydroxides, ammoniumhydroxide and so on in the proportion of up to 50 percent by weight ofthe total base when the particular type of wood can withstand suchwatersoluble bases without reacting therewith to form stains.

The base deposit is adhered to the lumber with a suitable binder oradhesive as a "wash coat" rather than a paint. The purpose of the binderhere is not to encase or encapsulate the base particle to form aconventional paint coating, but rather adhere or glue the deposit to thelumber so that it will not be dislodged from the lumber by the forces ofthe rain, wind and normal abrasion occasioned during the course of thejourney. The binder should not be present in an amount that would tendto encapsulate the deposit thus acting as a barrier between theatmospheric moisture and the particle to prevent or inhibit leaching.

Pigments and fillers can also be used in admixture with the baseparticles to obtain properties such as thixotropy, coloration, stabilityand other properties. Thus, supplemental pigments such as titania,silica, iron oxide, zirconia and other pigmentary or filler materialscan be included in the coating composition along with the base andbinders.

The binder can be any thermoplastic or thermosetting composition insolution, dispersion, suspension or emulsion in organic or aqueoussolvent. The selection of the binder is not particularly critical aslong as the binder is compatible with the base particles, wets thewater-repellent coating, and is capable of curing to adhere the depositof particulate base to the waterrepellent lumber substrate. Curing asused herein means that the binder forms as adherent residue on drying,heating or otherwise processing. Curing does not necessarily infercross-linking exclusively, but it can include coalescence as upon dryinga latex.

Suitable film-forming binders include the natural or conventionalpigment binders such as casein; glues, gelatin; starch; polyvinylalcohol; gums and cellulose esters and ethers (e.g., carboxy methylcellulose, sodium carboxy methyl cellulose, cellulose acetate andhydroxy ethyl cellulose). Some of these binders tend to be watersensitive or water soluble and are usually used with water-insolublebinders. The binders can be of the same type as the water-repellentcoating materials mentioned above and are applied directly thereover.These binders are in a vehicle which wets" the waterrepellent coating onthe lumber so that there is no tendency to bead up on thewater-repellent coating which results in localized deposits ofatinctorial slowleaching base. Such a vehicle can be a solvent solution(e.g., in aromatic hydrocarbons such as toluene and xylene; aliphaticssuch as hexane, octane or cycloaliphatics such as cyclohexane; alcoholssuch as methanol and ethanol, or even in solution in a vinyl monomerpolymerization with ethylenic unsaturation present in the film formingresins). Water solution or aqueous latex can be used if they containsufficient wetting agent so that the water-repellent coating wets outrather than beading up." Usually organic solvent vehicles are used forefficiency and economy.

For application, a coating composition comprising a slurry or dispersionof base particles (with or without pigments and fillers) and binder inan aqueous or organic solvent carrier is prepared according to the usualmixing techniques for preparing conventional pigment in binderdispersions using conventional anti-foam agents, dispersing agents,wetting agent and emulsifi- EXAMPLE PART A A concentrate for awater-repellent coating composition is prepared by thoroughly blendingthe following ingredients in an agitated vessel at a temperature between80 and 100F. until a stable dispersion is formed:

Percent lly Weight Ingredient Parts (Approximate) Water 2,850 59 Anionicpolyelectrolyte dispersing agent 1 l8 2 Brown oxide pigment 550 I 1Hydroxycthyl cellulose thickener 16 0.3 Ammonium hydroxide 7 Triethanolamine 40 0.7 Emulsified paraffin wax having a melting point of 1,300 ofwax solids 27 125 to 135F. and an average particle size of 1 to 2microns ers, as required, so that the coating wets the waterrepellentcoated lumber.

The coating composition can be prepared in the form of a concentrate ofthe base particles in binder and carrier containing as much as 2 to 75percent by weight of base particles for subsequent dilution with wateror solvent at the point of application. The base particle concentrationof the coating as applied to the lumber is about 0.1 to 10 percent byweight and preferably about 0.1 percent to about 5 percent by weight ofthe coating composition together with sufficient binder to adhere thebase particles to the waterrepellent coated lumber. About 1 part byweight of binder is sufficient to bind up to parts by weight of baseparticles plus pigment (if any). Usually about 1 part by weight ofbinder is used for every 1 to 6 parts by weight of base particles pluspigment to achieve effective adhesion to the lumher.

The coating composition can be applied to the waterrepellent coatedlumber by conventional coating means, such as brushing, spray coatings,roller coating, dip coating, air doctoring and the like. For mostapplications where the period of exposure is up to six months, thecoating composition is applied to the surface of the lumber to beprotected in the proportion of about 0.001 U.S. gallon/foot to about0.01 US.

PART B A coating composition for direct application to thewater-repellent coated lumber of Part A is prepared by thoroughlyblending the following ingredients in an agitated vessel at atemperature between to F. until a stable dispersion if formed. Thiscoating composition wets the water-repellent coated lumber and is readyfor direct application to the waterrepellent coated lumber as is, andrequires no further dilution at the point of application. Furthennore,this coating composition is adapted for use at very low temperaturesbelow the freezing point of water in that the carrier is an organicsolvent (mineral spirits), so freezing is not a problem.

PART B Percent by Weight Ingredient Parts (Approximate) Particulate Baseand Pigment Lime (calcium oxide having a particle size of 100% passing35 mesh and 79% passing 350 mesh) 9 2.5

Alkaline-earth base [barium metaborate pigment (81:8 0., H O) having aspecific gravity of about 3.3, solubility in water of 0.4%, maximum at70F. and an average particle size of about 5 to 10 microns] 13 3.5

Water-dispersible white pigment grade rutile titania (pigmentaryparticle size and quality) 2 0.5

PART B Continued Percent by Weight Ingredient Parts (Approximate)Binders Petroleum hydrocarbon wax (a paraffinic petroleum-basedhydrocarbon distillate wax having a molecular weight of about 500 to[,000,

a melting point of about l25 to l75F., such as obtained by dewaxingpetroleum-based lubricating oils) 9 2.5

Wetting Agent Aluminum stearate 0.3

Mineral spirits (a light hydrocarbon liquid having a distillation rangeof about 300F. to 400F., an API gravity of 45 to 49.5,

a specific gravity of about 0.8).

During the blending, the petroleum hydrocarbon wax disperses in themineral spirits to yield a coating composition having a specific gravityof about 0.85 containing about 9 percent by weight of non-volatilematerials.

The coating composition is sprayed with a spray-gun type applicator ontothe exposed surface of waterrepellent coated lumber of PartA loaded forrail shipment in an open flatcar of steel construction in a train ofsimilarly loaded flatcars. The coating composition is sprayed at therate of 0.005 to 0.004 U.S. gallon/foot of exposed coated lumber surfaceat ambient outdoor temperature of about 70F. Upon standing the solventdries to leave a deposit of lime, barium metaborate and white titaniapigment adhering to the water-repellent coated lumber by the petroleumwax binder. The white titania pigment gives the coating an appearance ofa very dilutewhitewash coating. The titania pigment is used so that thetreated areas can be distinguished from the untreated areas.

The trainload of treated lumber travels a distance of 2,000 miles inexposed, condition in the open flatcar over a 2- to 3-week period. Atthe end of the journey, transit stain is not visible on the lumbertreated by both Part A and Part B, while water-repellent lumber treatedby Part A only has a dark brown spotty" stain on the water-repellentcoating. The brown stains are apparently in those areas when waterdroplets have evaporated. The surface pH on the lumber treated by PartsA and B is tested byrnoist pH paper and is observed to be between about10 and 11. This example shows the combination of lime and bariummetaborate are effective as the particulate base in retarding transitstain in water-repellent treated lumber. When this example is repeated,except that borax or calcium oxide or magnesium oxide are substitutedforthe barium metaborate as the base, similar results are obtained.

Similar results are obtained when this example is repeated using a 10percent by weight aqueous emulsion of polyolefin wax such as anemulsifiable polyethylene wax having a melting point of 213 to 221F. andan Acid Number of 14 to 1? sold by Allied Chemical under the name ACpolyethylene 629 in the waterrepellent coating of Part A.

Similar results are also obtained when a butadienestyrene latex such asLatex S12R by Dow Chemical containing 40 percent solids; or a vinylchloride latex containing 50 percent solids; or a polystyrene latexcontaining 40 percent solids on a polyvinyl acetate latex containing 50percent solids such as Gelva S-55 sold by Shawinigan; are substituted onan equivalents solids basis in the water-repellent coating of Part A.

Similar results are also obtained when the procedures of Examples 5, 6,and 7 of copending application Ser. No. 142,791 are repeated exceptusing lumber that has a water-repellent coating thereon.

Having thus described the invention, what is claimed l. [n the transitof lumber by rail wherein said lumber has a water repellent surfacecoating thereon and exposed surfaces of said lumber so coated have atendency for transit staining by metallic iron, the method for reducingthe tendency for discoloration of exposed coated surfaces and permittingunwrapped transit of the lumber which comprises the steps of;

applying to said exposed coated surfaces a suspension containing about0.1 to about 10 percent by weight of a relatively water-insolubleparticulate base, binder and a vehicle therefor wherein the weight ratioof binder to base particles plus pigment, if any, is in the range ofabout 1 part binder per 1 to 10 parts base particles plus pigment, saidvehicle being a compound which wets the waterrepellent coating and beingemployed in sufficient amount to prevent beading of said suspension onthe coating, curing said binder after application to produce abinder-starved layer on said exposed surfaces from which saidparticulate base is slowly leachable by water, v I

said base particles being atinctorial and present on said surfaces in anamount to maintain said surfaces at a pH above about 10 for the periodof tran- Slt,

said suspension being applied to the exposed coated surface of thelumber in the proportion of about 0.001 to about 0.01 US. gallons perfoot*,

said base having a solubility in water of at least about 0.001 percentbut less than 10 percent at 32F.

2. The method of claim 1 wherein at least a portion of said base has awater solubility between about 0.00l percent and 1 percent by weight inwater at 32F.

3 The method of claim 1 wherein said base is an alkaline-earth baseselected from the group consisting of oxides, carbonates, phosphates,hydroxides, borates, borosilicates and hydrates thereof, of magnesium,calcium and barium.

4. The method of claim 1 wherein said coating composition contains about0.l percent to about 5 percent by weight of said base particles.

5. The method of claim I wherein the weight ratio of binder to baseparticles plus pigment is in the range of prepared from a concentrate ofthe base particles in binder and carrier, such concentrate containingabout 2 percent to about percent by weight base particles.

9. The method of claim 1 wherein said vehicle comprises wetting agentsand emulsifiers so that the suspension wets the water-repellent coating.

10. The product prepared by the method of claim 1.

2. The method of claim 1 wherein at least a portion of said base has awater solubility between about 0.001 percent and 1 percent by weight inwater at 32*F.
 3. The method of claim 1 wherein said base is analkaline-earth base selected from the group consisting of oxides,carbonates, phosphates, hydroxides, borates, borosilicates and hydratesthereof, of magnesium, calcium and barium.
 4. The method of claim 1wherein said coating composition contains about 0.1 percent to about 5percent by weight of said base particles.
 5. The method of claim 1wherein the weight ratio of binder to base particles plus pigment is inthe range of about 1 part binder per 1 to 6 parts of base particles pluspigment.
 6. The method of claim 1 wherein said suspension is applied tothe surfaces of the lumber in the proportion of about 0.003 to about0.006 U.S. gallons per foot2.
 7. The method of claim 1 wherein said basehas a solubility in water of at least about 0.001 percent to about 0.5percent at 32*F.
 8. The method of claim 1 wherein said suspension isprepared from a concentrate of the base particles in binder and carrier,such concentrate containing about 2 percent to about 75 percent byweight base particles.
 9. The method of claim 1 wherein said vehiclecomprises wetting agents and emulsifiers so that the suspension wets thewater-repellent coating.
 10. The product prepared by the method of claim1.